Distribution of full motion video data has evolved from early television broadcasting to meet viewer demand. Earliest video distribution was by point-to-point wiring between a camera and a video monitor. This was followed by scheduled television broadcasting of programming over the public air waves. In the 1960's, Community Antenna Television (CATV) was chartered to provide off-air television signals to viewers in broadcast reception fringe areas. Later, under FCC regulation, the CATV industry was required to provide local access and original programming in addition to off-air broadcast signal distribution.
As a result, several sources of cable network programming were established. Because of the wide bandwidth available on cable television systems, additional channels were available for the new programming. However, programming wasgenerally prescheduled, with the viewer left to tune to the designated channel at the appointed time to view a particular program.
To increase revenues, cable television systems have initiated distribution of premium channels viewable only by subscribers having appropriate descramblers. The subscriber tunes the descrambler to receive a premium channel, descramble the video and audio information and supply a signal capable of reception on a standard television set. The variety of available programs, from broadcast networks such as CNN, ESPN, to specialized Pay-Per-View events, has prompted distribution networks to develop more efficient transmission and distribution techniques for information data including video, audio, text, and plain old telephone service (POTS).
Prior systems relied on wire transmissions to transmit analog signals within a limited bandwidth. For example, CATV video distribution systems have historically transmitted analog video information to homes and businesses using coaxial cable. There is a trend in the communications industries to develop digital systems in order to provide more efficient transmission of information. This development is found in digital cellular telephone systems, facsimile transmission systems, and video distribution systems. In particular, a number of systems have recently been proposed for distributing video information in compressed, digital data form.
In addition, several different wideband digital distribution networks have been proposed for offering subscribers an array of video services, including true Video On Demand service. The following U.S. patents disclose representative examples of such digital video distributions networks: U.S. Pat. Nos. 5,253,275 to Yurt et al., 5,132,992 to Yurt et al., 5,133,079 to Ballantyne et al., 5,130,792 to Tindell et al., 5,057,932 to Lang, 4,963,995 to Lang, 4,949,187 to Cohen, 5,027,400 to Baji et al., and 4,506,387 to Walter. In particular, Litteral et al. U.S. Pat. No. 5,247,347 discloses a digital video distribution network providing subscribers with access to multiple Video On Demand service providers through the public switched telephone network, as described in more detail below.
U.S. Pat. No. 5,247,347 to Litteral et al., assigned in common with the present invention and incorporated herein in its entirety by reference, integrates a public switched telephone network with video-on-demand service. Specifically, the disclosed video-on-demand system adopts existing components of the Public Switched Telephone Network (PSTN) and implements compression techniques to store video information for subsequent forwarding over interoffice facilities. The switching facilities are located in central offices (COs) serving residential customers or subscribers. Electronic devices associated with the subscriber loops modify the transmission characteristics of the subscriber loops to permit delivery of full motion video information over existing loop plant facilities.
The networks of the prior art typically have not been designed to accommodate a full range of digital services such as telephone, video, video-on-demand, data services, information services, interactive services, and other modern digital offerings.
A disadvantage of systems using the PSTN as a video distribution system is that they are often bandwidth limited, providing only still frame or video conferencing capabilities. Because the systems use the PSTN only for connectivity between subscribers and/or between subscribers and Video Information Providers (VIPs), there is no capability for dynamic routing of digitized video without requiring dedicated leased, wide bandwidth circuits.
Attempts have been made to improve the core switching, multiplexing and transmission technologies for integrated digital networks to support voice, data and video services from VIPs for multiple users. For example, fiber optic transmission systems with bandwidths ranging from 155.52 to 2,488.32 Mbps have been considered to improve bandwidth access. In addition, asynchronous transfer mode (ATM) has been developed as a technique to provide broad-bandwidth, low delay, packet switching and multiplexing. In ATM, usable capacity can be assigned dynamically (on demand) by allocating bandwidth capacity to fixed-sized information-bearing units called "cells". Each cell contains header and information fields. The ATM standard, CCITT.121/2 specifies a 53 byte cell which includes a 5 byte header and a 48 byte payload.
MPEG (moving picture experts group) is a broad generic standard for digital video program compression. A number of specific compression algorithms satisfy MPEG requirements. MPEG-2 is a second generation compression standard capable of encoding video program material into a 6 Mbits/sec bit stream and packetizing a number of 6 Mbits/sec channel streams into a single higher rate signal transport stream. The conversion of MPEG-2 data into ATM cell format, however, imposes additional overhead requirements that reduce the information-carrying capacity of the network. For example, certain transmission protocols may require a stream of continuous data. Thus, an ATM data stream carrying MPEG video data may need to be padded with ATM idle cells, or "dummy cells", in order to ensure proper synchronization with the physical layer. Therefore, the network's information-carrying efficiency is reduced each time information data is converted to another layer of transport.
In addition, there has been a growth of VIPs offering video services to subscribers. The growth in the number of VIPs offering services will result in capacity problems on the PSTN connecting the VIP services to their subscribers. In addition, any one VIP may not fully utilize the physical connection to the PSTN when providing video services. Thus, if a plurality of VIPs each use an assigned optical fiber at, for example, fifty percent capacity, the PSTN will be inefficiently utilized if the optical fiber of each VIP is connected to the PSTN internal switches. Thus, there is a need for increased bandwidth and efficient connectivity techniques in the PSTN as competition increases between VIPs for connectivity to subscribers.